X-Ray Pulsar Timing: Barycentric Delay Correction

Before a spacecraft can use millisecond X-ray pulsars as a natural deep-space clock or navigation beacon, it must correct every photon's arrival time for the Roemer delay (light-travel time across its own position vector) and the much smaller relativistic Shapiro delay from the Sun's gravity, converting a local detector timestamp into Solar System Barycentric time. This simulator renders a spacecraft moving through the inner solar system toward a real millisecond pulsar, computes both delays live from actual orbital geometry, and folds incoming photons into two side-by-side pulse profiles — one left uncorrected (which stays flat noise, since the delay is thousands of pulse periods) and one barycentric-corrected, which sharpens into a real peak unless a position-knowledge error is dialed in to smear it, illustrating exactly the precision bottleneck real XNAV timing pipelines face.